[CPMD-list] EMASS parameter

[Axel Kohlmeyer]

>>> "SL" == Sergei Lisenkov <proffess at yandex.ru> writes:

SL> Dear CPMD users,

hello sergey,

SL> I would like to do CP MD simulation of C60 fullerene. But I don't know how specify a parameter EMASS. If I use Vanderbilt potential, I got the positive total energy and process is disconverged, if I use TM pseudo (norm conserving) I have either big temperature nor normal temperature but after 19 steps I have 
SL>  1  0.01620   264.2    -341.50698    -341.43294    -341.41674   0.000   33.98
SL>          2  0.85635   393.9    -341.12511    -341.01473    -340.15838   0.000   35.84
SL>          3249.61712   552.5    -277.63505    -277.48020     -27.86309   0.001   31.53

two observations: your md is obviously 'diverging' and your starting
structure seems to be not the 'equilibrium' structure.

to 'stabilize' the md you would need to decrease the timestep
or increase the emass parameter or both. what value is appropriate 
one usually has to find by experimenting. please keep in mind, that 
when increasing EMASS the electrons will 'lag' behind more.
e.g. an EMASS value of 800.0 is already considered large.

but since the system also seems to pick up a lot of kinetic 
energy fast, i would suggest to first perform a (not too precise) 
geometry optimization and then start the md run from that structure. 

alternatively, if you are not too far away from equilibrium,
you may get away by simply using something like 
TEMPCONTROL IONS
  200 50.0
to quickly remove the kinetic energy from your ionic system
until it has equilibrated.

hope this helps,
     axel kohlmeyer.

SL>          4NaN      NaN     NaN           NaN           NaN              0.00018234.06
SL>          5NaN      NaN     NaN           NaN           NaN           NaN     19076.24
SL>          6NaN      NaN     NaN           NaN           NaN           NaN     18673.92
SL>          7NaN      NaN     NaN           NaN           NaN           NaN     19155.86
SL>          8NaN      NaN     NaN           NaN           NaN           NaN     18557.44
SL>          9NaN      NaN     NaN           NaN           NaN           NaN     18030.04
SL>         10NaN      NaN     NaN           NaN           NaN           NaN     18994.91
SL>         11NaN      NaN     NaN           NaN           NaN           NaN     17752.60
SL>         12NaN      NaN     NaN           NaN           NaN           NaN     18013.25
SL>         13NaN      NaN     NaN           NaN           NaN           NaN     19568.40
SL>         14NaN      NaN     NaN           NaN           NaN           NaN     18188.09
SL> or problems in the parameter MAXIT (31 > 30). 
SL> How to solve it?

if you see those NaNs, doom is close. ;-)

SL> Thank you very much,
SL> Sergey
SL> _______________________________________________
SL> CPMD-list mailing list
SL> CPMD-list at cpmd.org
SL> http://www.cpmd.org/mailman/listinfo/cpmd-list



--

=======================================================================
Axel Kohlmeyer       e-mail: axel.kohlmeyer at theochem.ruhr-uni-bochum.de
Lehrstuhl fuer Theoretische Chemie          Phone: ++49 (0)234/32-26673
Ruhr-Universitaet Bochum - NC 03/53         Fax:   ++49 (0)234/32-14045
D-44780 Bochum  http://www.theochem.ruhr-uni-bochum.de/~axel.kohlmeyer/
=======================================================================
If you make something idiot-proof, the universe creates a better idiot.